1 The completeness of data on trailer registrations varies greatly among states. Data are reported to the extent available and, in some cases, are supplemented by estimates of the Federal Highway Administration.

2 This column includes all commercial type vehicles and semi-trailers that are in private or for-hire use.

3 Several states do not require the registration of light farm or automobile trailers.

4 Some states may not require the registrations of mobile homes and house trailers. In states where this classification is not available, house trailers are included with light car trailers.